1. Field of the Invention
The present invention generally relates to a camera lens assembly, and in particular, to an optical image stabilizer for stabilizing an image blurred by movement when a digital camera or an optical device mounted in a mobile communication terminal photographs a subject.
2. Description of the Related Art
With the miniaturization of digital cameras and development of lightweight techniques, mobile communication terminals or devices having optical lenses and camera devices have come into wide use.
As the mobility of a camera lens assembly mounted in a mobile communication terminal increases, image blurring caused by fine vibration or handshaking represents a serious impediment to high quality images. Moreover, frequent photographing during movement increases a need to correct for movement or vibration such as handshaking.
Although high-definition cameras have emerged with the development of optical technology, they lose half their effect due to image blurring caused by vibration, thus, increasing a need for an image stabilizer.
Image stabilizing techniques can be roughly classified into two types. One of them is an electric image stabilization technique, i.e., digital image stabilization (DIS), and electronic image stabilization (EIS), in which blurring is detected from a captured image, data stored in a camera device or a memory, is corrected, and the camera device receives a blurred image and generates a clear image by adjusting a position and a color electrically or using a program.
The electric image stabilization technique does not require high cost because there is no need for separate mechanical and physical configurations and it is easy to adopt due to few constraints on its structure. However, adjustment using a program requires a separate memory or a high-performance camera device. Moreover, a photographing speed may decrease as time required for correcting of a blurred image increases. In addition, the extent to which an afterimage is removed using a program is limited, resulting in degradation of correction.
The second type is referred to as optical image stabilization (OIS). An optical image stabilizer detects user's movements or handshaking and changes the position of an optical lens or a camera device in relation. Therefore, blurring of the image formed in the camera device from vibrating is prevented even in the occurrence of vibration of a photographing device.
In the case of the optical image stabilizer, installation of a separate correction device increases a manufacturing cost and requires an installation space. However, the optical image stabilizer can project a clear image on a camera device and remove an afterimage, thereby maintaining a correction rate of 90% or more. In addition, when camera devices having the same performance are used, the camera device using the optical image stabilizer can capture a clearer image than the camera device using the electric image stabilizer. For these reasons, an optical image stabilizer is more widely used than an electric image stabilizer in a photographing device with high-resolution requirements.
A correction technique using movement of an optical lens can be used in a digital camera or device having a space that is sufficiently large to have a driving unit for driving the optical lens. But there is a limit in using the correction technique for a small-size digital camera or mobile communication terminal having space constraints. To solve the problem, a technique for correcting for vibration by moving a camera device has been actively studied.
Japanese Patent Publication No. Hei. 10-39350 discloses an optical handshaking correction device. In the disclosed handshaking correction device, an X-axis piezoelectric element and a Y-axis piezoelectric element are arranged on the contour of an optical lens and a separate support is provided to support the X-axis and Y-axis piezoelectric elements, thereby causing the optical lens to contact with the driving axis of the X-axis or Y-axis piezoelectric element according to the extent of blurring of a captured image and moving the optical lens by a predetermined distance using frictional force. As such, to install a driving device such as a piezoelectric element on the contour of the optical lens, the outer diameter of the optical lens must be sufficiently large. As a result, the handshaking correction device is difficult to mount on a mobile communication terminal where the length and outer diameter of a camera lens assembly are extremely limited.
Moreover, in order to drive an optical lens having a predetermined weight, a significant amount of driving force should be generated, causing a difficulty in miniaturization of a driving device. In addition, a great deal of power is required, thus, making it difficult to mount the handshaking correction device on a portable photographing device using a rechargeable battery.
Furthermore, a difficulty in designing a small-size driving device and a raise in the manufacturing cost caused by an increase in the number of parts impede the cost competitiveness of a photographing device having the handshaking correction device embedded therein.
Moreover, in the case of a contact driving device such as a piezoelectric element using frictional force with its driving axis, it is difficult to control the tolerance of a contact face and secure reliability due to malfunction resulting from abrasion of the contact face. In addition, a driving circuit for generating and applying a specific voltage waveform is required to drive the driving device such as a piezoelectric element, thus further increasing the manufacturing cost and imposing a limitation on the miniaturization of a photographing device.